1. Field of the Invention
The present invention relates generally to the manufacture of continuous seam-welded metal tubes or pipes, and more particularly to a system for obtaining the axial alignment of the weld seam in seam welded pipe or tube.
2. Description of the Prior Art
In accordance with a well-known procedure for fabricating seam-welded pipes and tubes, a continuous strip or skelp is advanced through a forming apparatus and progressively deformed into a tubular form having an open, longitudinally extending seam. The tubular form then advances through a welding station wherein the adjacent longitudinal free edges are urged together and joined by a suitable welding process. The particular process to be employed will generally be dictated by, among other factors, the material from which the tube or pipe is formed. For example, the pipe may be formed of low carbon steel, stainless steel, aluminum, etc., and the welding process may include any of the well-known welding techniques conventionally employed with the various materials. In a widely used embodiment the tube or pipe is heated by electrical induction so that the edges achieve fusion temperature, and the heated edges are urged into engagement to produce a continuous monolithic welded seam.
Following the welding step, the pipe or tube may advance through a scarfing unit for removal of the raised bead created incident to the formation of the welded seam, and then through a series of sizing rolls for imparting the precise diameter and cross-sectional configuration to the formed pipe. Finally, after the continuous pipe has been sized and cooled, it enters a cut-off mechanism wherein it is cut into sections of appropriate length.
Due, among other factors, to residual stresses in the material following formation of the pipe, and the heating and cooling incident to the welding of the seam, the pipe may tend to warp or snake and develop an undesirable non-linear configuration as it exits the constraints of the forming and welding mechanism. In order to minimize the amount of this curvature in the finished product, the pipe or tubing is directed through a straightening unit wherein appropriate forces are applied by straightening rolls to bend the pipe to compensate for existing curvature and cause it to assume a linear profile as it exits the forming apparatus. Heretofore, the pipe has been observed at some distance downstream from the straightening unit by an operator to visually determine the amount and orientation of existing curvature, and the straightening unit is then manually adjusted in response to the observed condition to compensate for the curvature. The procedure functions well for its intended purpose, and permits production of pipe of good quality. However, it has not been found entirely satisfactory in that it is dependent upon the operator's visual observation and subsequent manual adjustment of the straightening unit. It is thus subject to the operator's judgment, as well as human error. In addition, deviation of the pipe is best observed at some distance downstream from the straightening unit, typically in the cutoff area. Since the pipe advances at a relatively rapid rate, a significant amount of defective pipe may be produced between the time at which deviation is noted and corrective action can be taken at the straightening unit.
Also, the prior art has provided, as in U.S. Pat. No. 5,309,746 issued in the name of Nelson D. Abbey III, an alignment sensor immediately downstream from the straightening unit for continuously precisely determining the position of the advancing pipe relative to reference axes. Signals indicative of the observed position of the pipe relative to a predetermined desired position are generated, and the straightening unit is adjusted in response to the generated signals to shape the pipe so that it advances through the alignment sensor at the desired position.
In order to further insure the straightness of the pipe being produced, following severing of the continuous pipe into individual sections, some or all of the individual sections may be checked for straightness. The straightening unit is adjusted in response to observed deviations from straightness to insure that the finished product is within precise limits of axial straightness. To that end, following severance from the continuous pipe the individual pipe sections are received on a deflection checker. The section is rotated about its longitudinal axis to position the weld seam at a predetermined position for reference purposes by means of a seam locator. With the seam position thus determined, deviation from straightness of the mid region of the pipe section is determined along orthogonal axes. Signals indicative of the direction and magnitude of deflection, or bow, are generated and transmitted to the straightening unit. The straightening unit is adjusted in response to the signals so as to correctly shape the continuous pipe to eliminate, or at least minimize, any deflection or bow in subsequent individual sections.
The formation of a continuous seam welded tube which is straight and the longitudinally extending seam is maintained in continuous direct alignment is a major objective of the present invention.